//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 20946 SUBJECT: GRB 170331A: Swift detection of a burst DATE: 17/03/31 01:53:22 GMT FROM: Scott Barthelmy at NASA/GSFC A. Melandri (INAF-OAB), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), P. D'Avanzo (INAF-OAB), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team: At 01:40:46 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 170331A (trigger=744791). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 323.782, -24.414, which is RA(J2000) = 21h 35m 08s Dec(J2000) = -24d 24' 48" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a complicated set of overlapping peaks with a total duration of about 25 sec. The peak count rate was ~1400 counts/sec (15-350 keV), at ~5 sec after the trigger. The XRT began observing the field at 01:42:50.6 UT, 124.2 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source located at RA, Dec 323.79260, -24.38604 which is equivalent to: RA(J2000) = 21h 35m 10.22s Dec(J2000) = -24d 23' 09.7" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 105 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (4.65 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.1 (+3.11/-2.65) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 127 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.05. Burst Advocate for this burst is A. Melandri (andrea.melandri AT brera.inaf.it). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 20948 SUBJECT: GRB 170331A: Prompt enhanced Swift-XRT position DATE: 17/03/31 02:31:40 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Using promptly downlinked XRT event data for GRB 170331A, we find an enhanced XRT position of the afterglow: RA, Dec: 323.7920, -24.3858 which is equivalent to: RA (J2000) = 21 35 10.08 Dec (J2000) = -24 23 08.9 with an uncertainty of 2.1 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/744791. Position enhancement is is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 20949 SUBJECT: GRB 170331A: LCO Sutherland observations DATE: 17/03/31 08:30:47 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy C. Guidorzi (U. Ferrara), S. Kobayashi, I.A. Steele (LJMU), A. Gomboc (U. Nova Gorica), C.G. Mundell (U. Bath) on behalf of a large collaboration report: We observed Swift GRB 170331A (Melandri et al. GCN 20946) on March 31, 03:21 UT (1.7 hours since the GRB) with two 1-m LCO units in Sutherland (South Africa) with the SDSS i filter. We do not find any object within the prompt enhanced Swift-XRT error circle (Evans GCN 20948) down to i>17.5 mag (with an exposure of 2x120s) as calibrated against USNOB-1 nearby stars. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 20960 SUBJECT: GRB 170331A: Enhanced Swift-XRT position DATE: 17/03/31 15:54:30 GMT FROM: Phil Evans at U of Leicester J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 1885 s of XRT Photon Counting mode data and 1 UVOT images for GRB 170331A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 323.79186, -24.38626 which is equivalent to: RA (J2000): 21h 35m 10.05s Dec (J2000): -24d 23' 10.5" with an uncertainty of 1.6 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 20962 SUBJECT: GRB 170331A: Swift-XRT refined Analysis DATE: 17/03/31 17:20:27 GMT FROM: Phil Evans at U of Leicester S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), A. Cholden-Brown (PSU) and report on behalf of the Swift-XRT team: report on behalf of the Swift-XRT team: We have analysed 7.4 ks of XRT data for GRB 170331A, from 127 s to 19.2 ks after the BAT trigger. The data comprise 12 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=0.99 (+0.12, -0.10). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.5 (+/-0.3). The best-fitting absorption column is 5.6 (+1.7, -1.5) x 10^21 cm^-2, in excess of the Galactic value of 4.7 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (7.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 5.6 (+1.7, -1.5) x 10^21 cm^-2 Galactic foreground: 4.7 x 10^20 cm^-2 Excess significance: 5.8 sigma Photon index: 2.5 (+/-0.3) If the light curve continues to decay with a power-law decay index of 0.99, the count rate at T+24 hours will be 1.1 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.7 x 10^-14 (8.9 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00744791. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 20965 SUBJECT: GRB 170331A: Swift/UVOT Upper Limits DATE: 17/03/31 23:34:37 GMT FROM: Paul Kuin at MSSL N. P. M. Kuin (UCL-MSSL) and A. Melandri (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 170331A 128 s after the BAT trigger (Melandri et al., GCN Circ. 20946). No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 20960) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 128 278 147 >20.4 u_FC 286 536 246 >19.6 white 128 1532 392 >21.0 v 616 1753 134 >18.5 b 542 1680 117 >19.1 u 286 1655 343 >19.7 w1 665 1631 117 >19.1 m2 1069 1606 58 >19.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.05 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 20967 SUBJECT: GRB 170331A: Swift-BAT refined analysis DATE: 17/04/01 06:15:10 GMT FROM: Amy Lien at GSFC C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), N. Gehrels (GSFC), H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC), A. Melandri (INAF-OAB), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 170331A (trigger #744791) (Melandri et al., GCN Circ. 20946). The BAT ground-calculated position is RA, Dec = 323.778, -24.406 deg which is RA(J2000) = 21h 35m 06.8s Dec(J2000) = -24d 24' 22.4" with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 18%. The mask-weighted light curve shows a weak pulse that starts at ~T-3 s, peaks at ~T+1 s, and ends at ~T+17 s. T90 (15-350 keV) is 17.57 +- 2.57 sec (estimated error including systematics). The time-averaged spectrum from T-2.78 to T+17.17 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.37 +- 1.19, and Epeak of 48.2 +- 12.7 keV (chi squared 61.51 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 9.7 +- 1.6 x 10^-7 erg/cm2 and the 1-sec peak flux measured from T+0.42 sec in the 15-150 keV band is 1.2 +- 0.4 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.86 +- 0.21 (chi squared 68.07 for 57 d.o.f.). All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/744791/BA/